I. Field of the Invention
The present invention relates generally to clocking circuits. More particularly, the present invention relates to asynchronous clocking of formatted data compatible with a synchronous general frame timing.
II. Description of the Related Art
Radiotelephones have become a prevalent means for users to keep in contact with land-line telephone systems. The radiotelephones communicate over a radio channel with fixed base stations that are connected to the land-line telephone network.
There are many different radiotelephone systems in operation. These systems can be divided generally into analog and digital radiotelephone systems. The analog systems typically communicate with frequency division multiple access (FDMA) modulated signals while the digital systems transmit data frames using various types of digital transmission techniques.
Some time division multiple access (TDMA) type radiotelephones, such as ones designed according to the European Digital Enhanced Cordless Telecommunications (DECT) 300 175 specification from the European Telecommunications Standard Institute (ETSI), use timers that are fixed to a certain full slot data framing. As the need develops for shorter or longer slots, such as half slots or double slots, due to the addition of digital transmission features, the timing must be adapted to be able to receive and transmit these various length slots. A radiotelephone with a fixed timer will not be able to operate in a system with more than one slot size.
Additionally, if a radiotelephone is in contact with a first base station and later changes to another system's base station, the new base station will not be synchronized An example of this is when a cordless telephone is using an office building's cordless PBX and the user walks into the street where the telephone logs onto the cellular system, the cellular system has different timing than the PBX system. This causes problems for a fixed timing radiotelephone since the frames are coming in asynchronously. Also, fading and bouncing of signals off terrain and buildings will inject delays in receiving data; the data is received later than expected. There is a resulting need for an asynchronous timer to enable asynchronous communication, allow variable delays between transmit and receive data packets, and to maintain an asynchronous connection during a certain time.